1. Field of the Invention
The present invention relates to a magnetic head assembly and a magnetic tape drive unit and a magnetic disk drive unit using such magnetic head assembly, more specifically to a technology for increasing recording density by reducing side erasing regions due to recording magnetic flux fringing in a magnetic recording head that is fabricated in a thin film fabrication process.
2. Description of Related Art
A magnetic recording head comprises first and second magnetic cores made from magnetic materials and a coil for inducing a recording magnetic flux in these two magnetic cores, thereby developing a leakage magnetic flux between tips of these two magnetic cores.
Then, a recording medium is arranged to travel in the condition that the recording medium is in contact with or at adjacent to the tips of these magnetic cores. Application of a recording signal to the above-mentioned coil results in recording a magnetic signal on the recording medium.
Incidentally, as the recording density becomes increasingly high in recent years, there arise strong V needs for reducing the dimension or pitch of the recording tracks in the width direction thereof in the recording medium. In order to achieve this objective, it is required to reduce the width of the magnetic recording cores constituting the magnetic recording head, thereby leading to the development of the fabrication technology of so-called thin film fabrication process for the magnetic recording head. And the magnetic recording head fabricated in such thin film fabrication process is practically applied to hard disk drive units.
FIG. 19 and FIG. 20 illustrate a magnetic recording head (a) which is used in a hard disk drive unit. The magnetic recording head (a) comprises a slider (c) as a substrate for floating the magnetic recording head (a) during the time when a disk shaped recording medium (b) is traveling. The slider (c) is formed with a first magnetic core (d) and a second magnetic core (f) formed on the first magnetic core (d) having a non-magnetic film (e) between them (see FIG. 19).
The magnetic recording head (a) having the above configuration is disposed below a back edge of the slider (c). It is to be noted here that the back edge of the slider (c) means an end portion at a backward position of a traveling direction of the disk shaped recording medium (b).
Accordingly, the first magnetic core (d) is at a leading side of the disk shaped recording medium (b) as compared to the second magnetic core (f) at the time of recording a magnetic signal and thus the second magnetic core (f) is at a trailing side (see FIG. 19 and FIG. 20).
As a result of air flow caused by the traveling of the disk shaped magnetic recording medium (b), the slider (c) of the magnetic recording head (a) of the hard disk drive unit is in a condition floating from the disk shaped recording medium (b). And the magnetic recording head (a) is brought to a condition approaching to the disk shaped recording medium (b) (non-contacting with the disc shaped recording medium (b)) (see FIG. 20).
Incidentally, it is typical in the above-mentioned magnetic recording head (a) that the first magnetic core (d) is made to be wider than the second magnetic core (f) (see FIG. 19).
In the following descriptions, the terms “wider film” and “narrower film” are respectively used to refer to relatively wider and narrower films by comparing relative width of two laminated films.
As illustrated in FIG. 21, it is easier in the film forming process to form on a base (wider film (g)) a film (narrower film (h)) having a narrower width than the base (see FIG. 21). However, if the wider film (g) is formed on the narrower film (h), both edges in the width direction overlap the both edge portions of the narrower film (h), thereby forming rounded portions and making it difficult to form a film in a desired shape, for example, elongated rectangular shape (see FIG. 22).
Accordingly, in order to form the wider film (g) on the narrower film (h), it is necessary to add a special step, for example, for forming a separate film (i) having the same thickness as the narrower film (h) along both edges thereof before forming the wider film (g) on both of the narrower film (h) and the separate film (i) (see FIG. 23).
However, it is not easy in such step to form the separate film (i) having the same thickness as the narrower film (h) along both right and left edges thereof. It is therefore difficult to form the wider film (g) of a desired shape on the separate film (i). For example, FIG. 24 shows an instance where the separate films (i) formed along both right and left edges of the narrower film (h) have thinner film thickness than that of the narrower film (h). On the contrary to the instance as shown in FIG. 24, if the thickness of the separate films (i) are thicker than the narrower film (h), the wider film (g) formed on the narrower film (h) tends to bend upwardly at both right and left edges, thereby making it difficult to obtain the wider film (g) in a desired shape.
Also, it is possible that gaps are occurred at junction portions between the narrower film (h) and the separate films (i). Even if the wider film (g) is formed on such films, the shape is different from the desired one (see FIG. 25).
Accordingly, in a case of fabricating the magnetic recording head (a) in the thin film fabrication process as described hereinabove, it is typical to fabricate the first magnetic core (d) to have a larger width than that of the second magnetic core (f).
Incidentally, as described hereinabove, the width of the first magnetic core (d) at the leading side in the magnetic recording head (a) is larger than that of the second magnetic core (f) at the trailing side. This increases the side erase regions due to the so-called recording magnetic flux fringing, thereby resulting in a poor S/N (signal-to-noise) ratio.
Describing more in detail, a magnetic signal to be recorded is developed by the leakage magnetic flux between the first magnetic core (d) at the leading side and the second magnetic core (f) at the trailing side. The leakage magnetic flux includes “α” developed at the edge portion (j) of the gap between the first magnetic core (d) and the second magnetic core (f) and “β” developed at both ends (k, k) between the first magnetic core (d) and the second magnetic core (f) (see FIG. 26).
Now, the leakage magnetic flux “α” developed at the edge portion (j) of the magnetic gap between the first magnetic core (d) and the second magnetic core (f) is oriented in parallel with the traveling direction of the disk shaped recording medium (b) with respect to the edge portion (j) of the magnetic gap of the second magnetic core (f). The magnitude of the leakage magnetic flux is the maximum in the magnetic gap but sharply decrease from the edge portion (j) of the second magnetic core (f) to the trailing side. Accordingly, a recording pattern that is recorded by the leakage magnetic flux “α” developed between the first magnetic core (d) and the edge portion (j) closer to the magnetic gap of the second magnetic core (f) is as illustrated in FIG. 27 by “γ”, or substantially following a shape along the edge-portion (j) closer to the magnetic gap of the second magnetic core (f).
In contrast to the above, the leakage magnetic flux “β” that is developed between the first magnetic core (d) and the both ends (k, k) in the width direction of the second magnetic core (f) has an angle which is perpendicular or close to perpendicular to the traveling direction of the disk shaped magnetic recording medium (b) with respect to the both ends (k, k) in the head width direction of the second magnetic core (f). The magnitude of the leakage magnetic flux decreases gradually from the junction to the edge portion (j) closer to the magnetic gap along the both ends (k, k) in the head width direction of the second magnetic core to the trailing side. Accordingly, a recording pattern as recorded by the leakage magnetic flux “β” that is developed between the first magnetic core (d) and the both sides (k, k) in the head width direction of the second magnetic core (f) is largely extended toward the trailing side rather than the junction to the edge portion (j) closer to the magnetic gap of the second magnetic core (f) as shown by a shape (m) in FIG. 27.
As a result, when the magnetic signal is recorded, there occur the portion “γ” due to the above-mentioned leakage magnetic flux “α” and the portions (m, m) extending backwardly like tails from both sides for a single bit pattern “l” because of the difference in orientations of the leakage magnetic flux “α” for the edge portion (j) closer to the magnetic gap of the second magnetic core (f) and the leakage magnetic fluxes “β” at both sides in the head width directions of the second magnetic core (f), and the difference in rates of reducing magnitudes of the leakage magnetic fluxes in the traveling direction of the disk shaped recording medium (b) (see FIG. 27). FIG. 27 illustrates concept of a single bit recording pattern “l”. Apparently, FIG. 27 illustrates how the recording pattern “l” is extending backwardly in bands at the both side portions (m, m) in the track width direction of the recording pattern “l”.
It is conceivable that the phenomena occurs because the opposed portions in the traveling direction of the disk shaped recording medium (b) at both end portions at the leading side of the first magnetic core (d) (the wider magnetic core) do not exist in the second magnetic core (f) (the narrower magnetic core) at the trailing side.
And the above-mentioned band portions (m, m) (that may be referred to as extending portions below) for a single bit recording pattern “l” are overwritten on the previously recorded recording pattern “l” for the next preceding bit, thereby causing the so-called side erase and thus effectively reducing the width of the recording track and degrading the SIN ratio.
Concretely, assuming that a single bit recording pattern is, for example, 1.96 μm in width (which is approximately equal to the width of the first magnetic core (d)) and 1 μm in length in the direction of the recording track. The base end portions of the band portions (m, m) extending backwardly at both end portions are 0.21 μm in the width direction of the track and 0.4 μm in length (see FIG. 28).
If plurality bits of such recording pattern “l” having the above shape are formed, the band portions (m, m) of a recording pattern “l2” are overwritten on a recording pattern “l1” for the next previous bit, thereby decreasing the effective width of the recorded pattern “l1” of the bit to 1.96−0.21×2=1.54 μm (see FIG. 27).
This means that, despite the formation of the recording track by the magnetic core (the first magnetic core) (d) having the width of 1.96 μm, the effective width of the recording track is only 1.54 μm, thereby degrading the S/N ratio.
Technologies to prevent such recording magnetic flux fringing are disclosed, for example, in Japanese patent publication nos. 7-93711 and 11-306513.
FIG. 29 illustrates a simplified construction of the magnetic head (n) as disclosed in the above-mentioned Japanese patent publication no. 7-93711. The magnetic head (n) is a so-called merge type magnetic head having a magnetic reproducing head (o) and a magnetic recording head (p). One of the magnetic shields for the magnetic reproducing head and one of the magnetic cores of the magnetic recording head are made in common and the common magnetic member is referred to as an intermediate magnetic core.
The magnetic reproducing head (o) is fabricated by forming a magnetic shield (r) on a slider (substrate) (q) and also forming an intermediate magnetic core (t) on the magnetic shield (r) with an MR device (s) disposed therebetween. It is to be noted, however, that a non-magnetic member is formed between the magnetic shield (r) and the MR device (s) and between the MR device (s) and the intermediate magnetic core (t).
On the other hand, the magnetic recording head (p) is fabricated by forming the above-mentioned intermediate magnetic core (t) and a magnetic core (u) on the intermediate magnetic core (t) with a non-magnetic member formed therebetween, wherein the width of the magnetic core (u) is wider than that of the intermediate magnetic core (t). It is to be noted that the non-magnetic member interposed between the intermediate magnetic core (t) and the magnetic core (u) acts as a magnetic gap for the magnetic recording head.
According to the magnetic recording head (p) having the above-mentioned configuration, the portion opposed in the traveling direction of the disk shaped recording medium (b) to the both end portions of the intermediate magnetic core (t) (the narrower magnetic core) at the leading side is located in the magnetic core (u) (the wider magnetic core) at the trailing side. As a result, the recording pattern by the leakage magnetic flux that is developed at both end portions of the intermediate magnetic core (t) (narrower magnetic core) at the leading side is recorded again by the leakage magnetic flux that is developed at the edge portion of the trailing side magnetic core (u) closer to the magnetic gap. In this case, the orientation of the leakage magnetic flux that is developed at the edge portion of the trailing side magnetic core (u) closer to the magnetic gap completely coincides with the traveling direction of the disk shaped recording medium (b). And the magnitude of the leakage magnetic flux sharply decreases as the distance increases from the edge portion of the magnetic core (u) closer to the magnetic gap to the trailing side. The recording pattern substantially follows the edge portion of the magnetic core (u) closer to the magnetic gap, thereby developing essentially no band portions (m, m) that were developed on the recording pattern “l” and thus overcoming the so-called side erase problem.
However, in the magnetic recording head (p) as disclosed in Japanese patent publication no. 7-93711, it is required to form on the intermediate magnetic core (t) the magnetic core (u) that is wider than the intermediate magnetic core (t). This encounters the above-mentioned fabrication problem of forming a wider film (g) on a narrower film (h) (see FIG. 22, FIG. 24 and FIG. 25).
On the other hand, FIG. 30 illustrates a simplified construction of the magnetic head (v) as disclosed in Japanese patent publication no. 11-306513. The magnetic head (v) is also the so-called merge type magnetic head having a magnetic reproducing head (w) and a magnetic recording head (x). Only difference of the magnetic head (v) from the magnetic head (n) as disclosed in the above Japanese patent publication no. 7-93711 is the shape of the intermediate magnetic core. Accordingly, the same reference numerals as those for the magnetic head (n) are used to refer to the other corresponding parts and their descriptions are omitted herein.
The intermediate magnetic core (y) of the magnetic head (v) has substantially the same width as the magnetic shield (r) of the magnetic reproducing head (w) and a protruding portion (z) having a narrower width than the width of the magnetic core (u) is formed at the portion opposed to the magnetic core (u) of the magnetic recording head (x).
According to the magnetic recording head (x) of the above configuration, the recording pattern by the leakage magnetic flux from the both edges of the protruding portion (z) (acting as the narrower magnetic core) of the intermediate magnetic core at the leading side is recorded again by the leakage magnetic flux that is developed at the edge portion closer to the magnetic gap side of the magnetic core (u) (the wider magnetic core) at the trailing side. In this case, the orientation of the leakage magnetic flux that is developed at the edge portion closer to the magnetic gap of the magnetic core (u) at the trailing side is completely equal to the traveling direction of the disk shaped recording medium (b) and the magnitude of the leakage magnetic flux sharply decreases at the location departing from the edge portion closer to the magnetic gap of the magnetic core (u) to the trailing side. Accordingly, the recording pattern substantially follows the shape of the edge portion closer to the magnetic gap of the magnetic core (u), thereby developing essentially no band portions (m, m) on the recording pattern “l” and thus overcoming the so-called side erase problem.
However, in the magnetic recording head (x) as disclosed in the Japanese patent publication no. 11-306513, the intermediate magnetic core (y) is wider than the magnetic core (u) which is formed on the above-mentioned protruding portion (z). Accordingly, the wider member (u) is formed on the narrower member (z), thereby encountering the fabrication problem of forming the wider film (g) on the narrower film (h) as described hereinabove by reference to FIG. 22 through FIG. 25.